Flexible polyurethane foams made from toluene diisocyanate (TDI) and polyester or polyether polyols, comprise a significant portion of the polyurethane foam industry. Because those foams are combustible, burn uncontrollably after ignition, there have been extensive efforts in that industry to produce foams that are flame retardant.
Open-cell flexible polyurethane foams are more difficult to flame-proof than closed-cell, rigid foams, because open-cell foams allow oxygen to be transferred through it to the location where the foam has been ignited. Also, such foams permit volatilized flame retardant to escape.
Many different methods have been taught in the prior art for flame retarding flexible polyurethane foams. Most of these methods involve addition to the foam reactants of a flame retardant prior to or during the polymerization reaction so that the flame retardant is uniformly distributed throughout the foam. A detailed discussion of that prior art is found in U.S. Pat. No. 3,933,693 to David C. Priest and John E. Brandien and in U.S. Pat. No. 4,194,068 to Denis P. Miller and Masachico Tamaki.
The Priest patent was directed to an improvement over the prior art. Specifically, Priest and Brandien discovered a method to incorporate DBNG in flexible polyether polyurethane foam systems without obtaining closed-cell structures. Prior art attempts to incorporate that glycol resulted in foams having closed-cell structures and physical properties unsuitable for many uses. However, this improvement over the prior art was restricted to foams made from TDI containing no more than about 76 percent by weight of the 2,4-toluene diisocyanate isomer. Priest and Brandien were unable to use higher concentrations of that isomer probably because use of DBNG in polyurethane foam systems, without a flame retardant plasticizer, contained an inherent problem with the inability of the foamer to obtain high porosity foam using higher concentrations of that isomer.
The Miller patent was also directed to an improvement over the prior art. Specifically, Miller and Tamaki discovered a method of incorporating a three-component flame retardant mixture of a bromohydrin of pentaerythritol, a polyhydric alcohol or polyol and an organophosphorous compound in polyurethane foam systems. In that regard, see particularly the description of the invention therein under the heading "Summary of the Invention" at column 3, lines 29 to 54 and column 4, lines 1 through 21.